How characters treat a stranger, and how you become someone they know.
A character who has never met you:
They may still have heard about you. If gossip about "a newcomer" has reached them, they'll have an impression of you before you've said a word, but not your name.
Introduce yourself, and they'll use your name from then on.
When the conversation ends, they form a memory of it, and from then on they've met you. In every later conversation they know your name, your backstory, and everything they remember about you.
Some things don't count as meeting you: hearing gossip, watching a scene you spectated, or events from the daily digest.
Old friends, siblings, exes and rivals don't need an introduction. Write a Player Backstory on the character's profile and they know you from the very first line: your name, and the history you wrote together. See NPC profiles.
Each person in a scene is a stranger or not on their own terms. You might walk into a tavern where the barkeep greets you by name and the traveler beside her has no idea who you are.
Your Description (personality and backstory) is only for people who've met you. A stranger can't know your history until they learn it. See Your player character.